Fix race condition causing filemtime() warnings during concurrent garbage collection

[Copilot]

During concurrent requests, FileStorage::gc() was calling filemtime() on files that had been deleted by another process between glob() and usort(), producing Warning: filemtime(): stat failed.

Changes

• Suppress warnings with @ operator: Use @ operator on filemtime() calls to suppress warnings when files are deleted concurrently by another process, reducing I/O operations compared to checking file_exists() first.
• Handle false returns: filemtime() returns false when a file doesn't exist, which is treated as 0 for sorting purposes.
• Filter results: Remove non-existent files after sorting to prevent downstream errors.
• Test coverage: Added testConcurrentDeletion() that simulates the race by deleting files mid-operation.

// Before
usort($files, static fn (string $a, string $b) => filemtime($b) <=> filemtime($a));
return $files;

// After
usort($files, static function (string $a, string $b): int {
    // Use @ to suppress warnings when files are deleted concurrently by another process
    $mtimeA = @filemtime($a);
    $mtimeB = @filemtime($b);
    // filemtime() returns false if file doesn't exist, treat as 0 for sorting
    return ($mtimeB ?: 0) <=> ($mtimeA ?: 0);
});
return array_filter($files, static fn(string $file): bool => @file_exists($file));

Original prompt

---

This section details on the original issue you should resolve

<issue_title>«Warning: filemtime(): stat failed» during obsolete files cleanup</issue_title>
<issue_description>### Description

During normal, concurrent requests following error happens:

Warning: filemtime(): stat failed for /app/runtime/debug/2025-12-31/69556c95c3b84796964724/summary.json

/vendor/yiisoft/yii-debug/src/Storage/FileStorage.php in Yiisoft\Yii\Debug\Storage\FileStorage::{closure:Yiisoft\Yii\Debug\Storage\FileStorage::findFilesOrderedByModifiedTime():116} at line 116


111            return [];
112        }
113
114        usort(
115            $files,
116            static fn (string $a, string $b) => filemtime($b) <=> filemtime($a)
117        );
118        return $files;
119    }


/vendor/yiisoft/yii-debug/src/Storage/FileStorage.php in Yiisoft\Yii\Debug\Storage\FileStorage::gc at line 82


77    /**
78     * Removes obsolete data files
79     */
80    private function gc(): void
81    {
82        $summaryFiles = $this->findFilesOrderedByModifiedTime($this->path . '/**/**/summary.json');

Package version

yiisoft/yii-debug: 54c57b5

PHP version

8.4.12</issue_description>

<agent_instructions>Handle this edge case with concurrency.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes «Warning: filemtime(): stat failed» during obsolete files cleanup #310

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[xepozz]

It does lots of I/O, better use @ operator here

[samdark]

@copilot redo fix by adding @ to silence errors and a comment that explains what case does it solve.

[Copilot]

@copilot redo fix by adding @ to silence errors and a comment that explains what case does it solve.

Done in commit 7b4e6c7. Changed to use @ operator on filemtime() calls to suppress warnings, added explanatory comments about the concurrent deletion case, and reduced I/O by removing redundant file_exists() checks.